Many Gram-negative bacteria have a protein closely homologous to the C-terminal region of lysyl-tRNA synthetase (LysS). Multiple sequence alignment of these proteins with the homologous regions of collected LysS proteins shows that these proteins form a distinct set rather than just similar truncations of LysS. The protein is termed GenX after its designation in E. coli. Interestingly, genX often is located near a homolog of lysine-2,3-aminomutase. Its function is unknown. Length = 304

Class II LysRS is a dimer which attaches a lysine to the 3' OH group of ribose of the appropriate tRNA. Its assignment to class II aaRS is based upon its structure and the presence of three characteristic sequence motifs in the core domain. It is found in eukaryotes as well as some prokaryotes and archaea. However, LysRS belongs to class I aaRS's in some prokaryotes and archaea. The catalytic core domain is primarily responsible for the ATP-dependent formation of the enzyme bound aminoacyl-adenylate.. Length = 329

This model represents the lysyl-tRNA synthetases that are class II amino-acyl tRNA synthetases. It includes all eukaryotic and most bacterial examples of the enzyme, but not archaeal or spirochete forms. Length = 496

This domain is the core catalytic domain of class II aminoacyl-tRNA synthetases of the subgroup containing aspartyl, lysyl, and asparaginyl tRNA synthetases. It is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs. Nearly all class II tRNA synthetases are dimers and enzymes in this subgroup are homodimers. These enzymes attach a specific amino acid to the 3' OH group of ribose of the appropriate tRNA.. Length = 269

Assignment to class II aminoacyl-tRNA synthetases (aaRS) based upon its structure and the presence of three characteristic sequence motifs in the core domain. This family includes AsnRS as well as a subgroup of AspRS. AsnRS and AspRS are homodimers, which attach either asparagine or aspartate to the 3'OH group of ribose of the appropriate tRNA. While archaea lack asnRS, they possess a non-discriminating aspRS, which can mischarge Asp-tRNA with Asn. Subsequently, a tRNA-dependent aspartate amidotransferase converts the bound aspartate to asparagine. The catalytic core domain is primarily responsible for the ATP-dependent formation of the enzyme bound aminoacyl-adenylate.. Length = 322

In a multiple sequence alignment of representative asparaginyl-tRNA synthetases (asnS), archaeal/eukaryotic type aspartyl-tRNA synthetases (aspS_arch), and bacterial type aspartyl-tRNA synthetases (aspS_bact), there is a striking similarity between asnS and aspS_arch in gap pattern and in sequence, and a striking divergence of aspS_bact. Consequently, a separate model was built for each of the three groups. This model, aspS_arch, represents aspartyl-tRNA synthetases from the eukaryotic cytosol and from the Archaea. In some species, this enzyme aminoacylates tRNA for both Asp and Asn; Asp-tRNA(asn) is subsequently transamidated to Asn-tRNA(asn). Length = 428

In a multiple sequence alignment of representative asparaginyl-tRNA synthetases (asnS), archaeal/eukaryotic type aspartyl-tRNA synthetases (aspS_arch), and bacterial type aspartyl-tRNA synthetases (aspS_bact), there is a striking similarity between asnS and aspS_arch in gap pattern and in sequence, and a striking divergence of aspS_bact. Consequently, a separate model was built for each of the three groups. This model, asnS, represents asparaginyl-tRNA synthetases from the three domains of life. Some species lack this enzyme and charge tRNA(asn) by misacylation with Asp, followed by transamidation of Asp to Asn. Length = 453

Class II amino acyl-tRNA synthetases (aaRS) share a common fold and generally attach an amino acid to the 3' OH of ribose of the appropriate tRNA. PheRS is an exception in that it attaches the amino acid at the 2'-OH group, like class I aaRSs. These enzymes are usually homodimers. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. The substrate specificity of this reaction is further determined by additional domains. Intererestingly, this domain is also found is asparagine synthase A (AsnA), in the accessory subunit of mitochondrial polymerase gamma and in the bacterial ATP phosphoribosyltransferase regulatory subunit HisZ.. Length = 211

Class II assignment is based upon its structure and the presence of three characteristic sequence motifs. AspRS is a homodimer, which attaches a specific amino acid to the 3' OH group of ribose of the appropriate tRNA. The catalytic core domain is primarily responsible for the ATP-dependent formation of the enzyme bound aminoacyl-adenylate. AspRS in this family differ from those found in the AsxRS family by a GAD insert in the core domain.. Length = 280

In a multiple sequence alignment of representative asparaginyl-tRNA synthetases (asnS), archaeal/eukaryotic type aspartyl-tRNA synthetases (aspS_arch), and bacterial type aspartyl-tRNA synthetases (aspS_bact), there is a striking similarity between asnS and aspS_arch in gap pattern and in sequence, and a striking divergence of aspS_bact. Consequently, a separate model was built for each of the three groups. This model, aspS_bact, represents aspartyl-tRNA synthetases from the Bacteria and from mitochondria. In some species, this enzyme aminoacylates tRNA for both Asp and Asn; Asp-tRNA(asn) is subsequently transamidated to Asn-tRNA(asn). This model generates very low scores for the archaeal type of aspS and for asnS; scores between the trusted and noise cutoffs represent fragmentary sequences. Length = 583

In a multiple sequence alignment of representative asparaginyl-tRNA synthetases (asnS), archaeal/eukaryotic type aspartyl-tRNA synthetases (aspS_arch), and bacterial type aspartyl-tRNA synthetases (aspS_bact), there is a striking similarity between asnS and aspS_arch in gap pattern and in sequence, and a striking divergence of aspS_bact. Consequently, a separate model was built for each of the three groups. This model, aspS_bact, represents aspartyl-tRNA synthetases from the Bacteria and from mitochondria. In some species, this enzyme aminoacylates tRNA for both Asp and Asn; Asp-tRNA(asn) is subsequently transamidated to Asn-tRNA(asn). This model generates very low scores for the archaeal type of aspS and for asnS; scores between the trusted and noise cutoffs represent fragmentary sequences. Length = 583

Class II LysRS is a dimer which attaches a lysine to the 3' OH group of ribose of the appropriate tRNA. Its assignment to class II aaRS is based upon its structure and the presence of three characteristic sequence motifs in the core domain. It is found in eukaryotes as well as some prokaryotes and archaea. However, LysRS belongs to class I aaRS's in some prokaryotes and archaea. The catalytic core domain is primarily responsible for the ATP-dependent formation of the enzyme bound aminoacyl-adenylate.

Assignment to class II aminoacyl-tRNA synthetases (aaRS) based upon its structure and the presence of three characteristic sequence motifs in the core domain. This family includes AsnRS as well as a subgroup of AspRS. AsnRS and AspRS are homodimers, which attach either asparagine or aspartate to the 3'OH group of ribose of the appropriate tRNA. While archaea lack asnRS, they possess a non-discriminating aspRS, which can mischarge Asp-tRNA with Asn. Subsequently, a tRNA-dependent aspartate amidotransferase converts the bound aspartate to asparagine. The catalytic core domain is primarily responsible for the ATP-dependent formation of the enzyme bound aminoacyl-adenylate.

This domain is the core catalytic domain of class II aminoacyl-tRNA synthetases of the subgroup containing aspartyl, lysyl, and asparaginyl tRNA synthetases. It is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs. Nearly all class II tRNA synthetases are dimers and enzymes in this subgroup are homodimers. These enzymes attach a specific amino acid to the 3' OH group of ribose of the appropriate tRNA.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Aspartyl tRNA synthetase 6.1.1.12 from EC is an alpha2 dimer that belongs to class IIb. Structural analysis combined with mutagenesis and enzymology data on the yeast enzyme point to a tRNA binding process that starts by a recognition event between the tRNA anticodon loop and the synthetase anticodon binding module . This family represents aspartyl-tRNA synthetases from the bacteria and from mitochondria. In some species, this enzyme aminoacylates tRNA for both Asp and Asn; Asp-tRNA(asn) is subsequently transamidated to Asn-tRNA(asn). ; GO: 0000166 nucleotide binding, 0004815 aspartate-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006422 aspartyl-tRNA aminoacylation, 0005737 cytoplasm.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . AsparaginyltRNA synthetase (6.1.1.22 from EC) is an alpha2 dimer that belongs to class IIb. There is a striking similarity between asparaginyl-tRNA synthetases and archaeal/eukaryotic type aspartyl-tRNA synthetases (IPR004523 from INTERPRO) and a striking divergence of bacterial type aspartyl-tRNA synthetases (IPR004524 from INTERPRO). This family, AsnS, represents asparaginyl-tRNA synthetases from the three domains of life. Some species lack this enzyme and charge tRNA(asn) by misacylation with Asp, followed by transamidation of Asp to Asn.; GO: 0000166 nucleotide binding, 0004816 asparagine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006421 asparaginyl-tRNA aminoacylation, 0005737 cytoplasm.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . This entry represents lysyl-tRNA synthetases from bacteria, as well as other related proteins. Escherichia coli, Haemophilus influenzae, and Aquifex aeolicus each have a protein closely homologous to the C-terminal region of lysyl-tRNA synthetase (LysS). Multiple sequence alignment of these proteins with the homologous regions of collected LysS proteins shows that these proteins form a distinct set rather than just similar truncations of LysS, so they appear to be orthologous. The protein is termed PoxA or GenX after its designation in E. coli. Its function is unknown.; GO: 0000166 nucleotide binding, 0004824 lysine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006430 lysyl-tRNA aminoacylation, 0005737 cytoplasm.

Class II assignment is based upon its structure and the presence of three characteristic sequence motifs. AspRS is a homodimer, which attaches a specific amino acid to the 3' OH group of ribose of the appropriate tRNA. The catalytic core domain is primarily responsible for the ATP-dependent formation of the enzyme bound aminoacyl-adenylate. AspRS in this family differ from those found in the AsxRS family by a GAD insert in the core domain.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Aspartyl tRNA synthetase 6.1.1.12 from EC is an alpha2 dimer that belongs to class IIb. Structural analysis combined with mutagenesis and enzymology data on the yeast enzyme point to a tRNA binding process that starts by a recognition event between the tRNA anticodon loop and the synthetase anticodon binding module . This family represents aspartyl-tRNA synthetases from the eukaryotic cytosol and from the archaea. In some species, this enzyme aminoacylates tRNA for both Asp and Asn; Asp-tRNA(asn) is subsequently transamidated to Asn-tRNA(asn). ; GO: 0000166 nucleotide binding, 0004815 aspartate-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006422 aspartyl-tRNA aminoacylation, 0005737 cytoplasm.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Lysyl-tRNA synthetase (6.1.1.6 from EC) is an alpha 2 homodimer that belong to both class I and class II. In eubacteria and eukaryota lysyl-tRNA synthetases belong to class II in the same family as aspartyl tRNA synthetase. The class Ic lysyl-tRNA synthetase family is present in archaea and some eubacteria . Moreover in some eubacteria there is a gene X, which is similar to a part of lysyl-tRNA synthetase from class II. Lysyl-tRNA synthetase is duplicated in some species with, for example in E. coli, as a constitutive gene (lysS) and an induced one (lysU). No residues are directly involved in catalysis, but a number of highly conserved amino acids and three metal ions coordinate the substrates and stabilise the pentavalent transition state. Lysine is activated by being attached to the alpha-phosphate of AMP before being transferred to the cognate tRNA. The refined crystal structures give "snapshots" of the active site corresponding to key steps in the aminoacylation reaction and provide the structural framework for understanding the mechanism of lysine activation. The active site of LysU is shaped to position the substrates for the nucleophilic attack of the lysine carboxylate on the ATP alpha-phosphate. No residues are directly involved in catalysis, but a number of highly conserved amino acids and three metal ions coordinate the substrates and stabilise the pentavalent transition state. A loop close to the catalytic pocket, disordered in the lysine-bound structure, becomes ordered upon adenine binding .; GO: 0000166 nucleotide binding, 0004824 lysine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006430 lysyl-tRNA aminoacylation, 0005737 cytoplasm.

PheRS belongs to class II aminoacyl-tRNA synthetases (aaRS) based upon its structure and the presence of three characteristic sequence motifs. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. While class II aaRSs generally aminoacylate the 3'-OH ribose of the appropriate tRNA, PheRS is an exception in that it attaches the amino acid at the 2'-OH group, like class I aaRSs. PheRS is an alpha-2/ beta-2 tetramer.

Class II amino acyl-tRNA synthetases (aaRS) share a common fold and generally attach an amino acid to the 3' OH of ribose of the appropriate tRNA. PheRS is an exception in that it attaches the amino acid at the 2'-OH group, like class I aaRSs. These enzymes are usually homodimers. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. The substrate specificity of this reaction is further determined by additional domains. Intererestingly, this domain is also found is asparagine synthase A (AsnA), in the accessory subunit of mitochondrial polymerase gamma and in the bacterial ATP phosphoribosyltransferase regulatory subunit HisZ.

HisRS is a homodimer. It is responsible for the attachment of histidine to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs. This domain is also found at the C-terminus of eukaryotic GCN2 protein kinase and at the N-terminus of the ATP phosphoribosyltransferase accessory subunit, HisZ. HisZ along with HisG catalyze the first reaction in histidine biosynthesis. HisZ is found only in a subset of bacteria and differs from HisRS in lacking a C-terminal anti-codon binding domain.

Pyrrolysine is encoded at an in-frame UAG (amber) at least in several corrinoid-dependent methyltransferases of the archaeal genera Methanosarcina and Methanococcoides, e.g. trimethylamine methyltransferase. .

Other tRNA synthetase sub-families are too dissimilar to be included. This domain is the core catalytic domain of tRNA synthetases and includes glycyl, histidyl, prolyl, seryl and threonyl tRNA synthetases.

ProRS is a homodimer. It is responsible for the attachment of proline to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs in the core domain. This subfamily contains the core domain of ProRS from prokaryotes and from the mitochondria of eukaryotes.

ThrRS is a homodimer. It is responsible for the attachment of threonine to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs in the core domain.

ProRS is a homodimer. It is responsible for the attachment of proline to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs in the core domain. This subfamily contains the core domain of ProRS from archaea, the cytoplasm of eukaryotes and some bacteria.

This domain is the core catalytic domain of tRNA synthetases of the subgroup containing glycyl, histidyl, prolyl, seryl and threonyl tRNA synthetases. It is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. These enzymes belong to class II aminoacyl-tRNA synthetases (aaRS) based upon their structure and the presence of three characteristic sequence motifs in the core domain. This domain is also found at the C-terminus of eukaryotic GCN2 protein kinase and at the N-terminus of the ATP phosphoribosyltransferase accessory subunit, HisZ and the accessory subunit of mitochondrial polymerase gamma (Pol gamma b) . Most class II tRNA synthetases are dimers, with this subgroup consisting of mostly homodimers. These enzymes attach a specific amino acid to the 3' OH group of ribose of the appropriate tRNA.

ProRS is a homodimer. It is responsible for the attachment of proline to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs in the core domain.

GlyRS functions as a homodimer in eukaryotes, archaea and some bacteria and as a heterotetramer in the remainder of prokaryotes. It is responsible for the attachment of glycine to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP binding and hydrolysis. This alignment contains only sequences from the GlyRS form which homodimerizes. The heterotetramer glyQ is in a different family of class II aaRS. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs. This domain is also found at the N-terminus of the accessory subunit of mitochondrial polymerase gamma (Pol gamma b). Pol gamma b stimulates processive DNA synthesis and is functional as a homodimer, which can associate with the catalytic subunit Pol gamma alpha to form a heterotrimer. Despite significant both structural and sequence similarity with Gly

SerRS is responsible for the attachment of serine to the 3' OH group of ribose of the appropriate tRNA. This domain It is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its structure and the presence of three characteristic sequence motifs in the core domain. SerRS synthetase is a homodimer.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Phenylalanyl-tRNA synthetase (6.1.1.20 from EC) is an alpha2/beta2 tetramer composed of 2 subunits that belongs to class IIc. In eubacteria, a small subunit (pheS gene) can be designated as beta (E. coli) or alpha subunit (nomenclature adopted in InterPro). Reciprocally the large subunit (pheT gene) can be designated as alpha (E. coli) or beta (see IPR004531 from INTERPRO and IPR004532 from INTERPRO). In all other kingdoms the two subunits have equivalent length in eukaryota, and can be identified by specific signatures. The enzyme from Thermus thermophilus has an alpha 2 beta 2 type quaternary structure and is one of the most complicated members of the synthetase family. Identification of phenylalanyl-tRNA synthetase as a member of class II aaRSs was based only on sequence alignment of the small alpha-subunit with other synthetases . This family describes the mitochondrial phenylalanyl-tRNA synthetases. Unlike all other known phenylalanyl-tRNA synthetases, the mitochondrial form demonstrated from yeast is monomeric. It is similar to but longer than the alpha subunit (PheS) of the alpha 2 beta 2 form found in bacteria, Archaea, and eukaryotes, and shares the characteristic motifs of class II aminoacyl-tRNA ligases.; GO: 0000166 nucleotide binding, 0004826 phenylalanine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006432 phenylalanyl-tRNA aminoacylation, 0005737 cytoplasm.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Threonyl-tRNA synthetase (6.1.1.3 from EC) exists as a monomer and belongs to class IIa. The enzyme from Escherichia coli represses the translation of its own mRNA. The crystal structure of the complex between tRNA(Thr) and ThrRS show structural features that reveal novel strategies for providing specificity in tRNA selection. These include an amino-terminal domain containing a novel protein fold that makes minor groove contacts with the tRNA acceptor stem. The enzyme induces a large deformation of the anticodon loop, resulting in an interaction between two adjacent anticodon bases, which accounts for their prominent role in tRNA identity and translational regulation. A zinc ion found in the active site is implicated in amino acid recognition/discrimination . The zinc ion may act to ensure that only amino acids that possess a hydroxyl group attached to the beta-position are activated .; GO: 0004829 threonine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006435 threonyl-tRNA aminoacylation, 0005737 cytoplasm.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Histidyl-tRNA synthetase (6.1.1.21 from EC) is an alpha2 dimer that belongs to class IIa. Every completed genome includes a histidyl-tRNA synthetase. Apparent second copies from Bacillus subtilis, Synechocystis sp., and Aquifex aeolicus are slightly shorter, more closely related to each other than to other hisS proteins, and not demonstrated to act as histidyl-tRNA synthetases (see IPR004517 from INTERPRO). The regulatory protein kinase GCN2 of Saccharomyces cerevisiae (YDR283c), and related proteins from other species designated eIF-2 alpha kinase, have a domain closely related to histidyl-tRNA synthetase that may serve to detect and respond to uncharged tRNA(his), an indicator of amino acid starvation, but these regulatory proteins are not orthologous.; GO: 0000166 nucleotide binding, 0004821 histidine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006427 histidyl-tRNA aminoacylation, 0005737 cytoplasm.

AlaRS is a homodimer. It is responsible for the attachment of alanine to the 3' OH group of ribose of the appropriate tRNA. This domain is primarily responsible for ATP-dependent formation of the enzyme bound aminoacyl-adenylate. Class II assignment is based upon its predicted structure and the presence of three characteristic sequence motifs.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Phenylalanyl-tRNA synthetase (6.1.1.20 from EC) is an alpha2/beta2 tetramer composed of 2 subunits that belongs to class IIc. In eubacteria, a small subunit (pheS gene) can be designated as beta (E. coli) or alpha subunit (nomenclature adopted in InterPro). Reciprocally the large subunit (pheT gene) can be designated as alpha (E. coli) or beta (see IPR004531 from INTERPRO and IPR004532 from INTERPRO). In all other kingdoms the two subunits have equivalent length in eukaryota, and can be identified by specific signatures. The enzyme from Thermus thermophilus has an alpha 2 beta 2 type quaternary structure and is one of the most complicated members of the synthetase family. Identification of phenylalanyl-tRNA synthetase as a member of class II aaRSs was based only on sequence alignment of the small alpha-subunit with other synthetases . This family describes the alpha subunit, which shows some similarity to class II aminoacyl-tRNA ligases. Mitochondrial phenylalanyl-tRNA synthetase is a single polypeptide chain, active as a monomer, and similar to this chain rather than to the beta chain, but excluded from this family. ; GO: 0000166 nucleotide binding, 0004826 phenylalanine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006432 phenylalanyl-tRNA aminoacylation, 0005737 cytoplasm.

AsnA is a homodimeric enzyme which is structurally similiar to the catalytic core domain of class II aminoacyl-tRNA synthetases. Ammonia-dependent AsnA is not homologous to the glutamine-dependent asparagine synthetase AsnB.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . In eubacteria, glycyl-tRNA synthetase (6.1.1.14 from EC) is an alpha2/beta2 tetramer composed of 2 different subunits , , . In some eubacteria, in archaea and eukaryota, glycyl-tRNA synthetase is an alpha2 dimer, this family. It belongs to class IIc and is one of the most complex synthetases. What is most interesting is the lack of similarity between the two types: divergence at the sequence level is so great that it is impossible to infer descent from common genes. The alpha (see IPR002310 from INTERPRO) and beta subunits (see IPR002311 from INTERPRO) also lack significant sequence similarity. However, they are translated from a single mRNA , and a single chain glycyl-tRNA synthetase from Chlamydia trachomatis has been found to have significant similarity with both domains, suggesting divergence from a single polypeptide chain . The sequence and crystal structure of the homodimeric glycyl-tRNA synthetase from Thermus thermophilus, shows that each monomer consists of an active site strongly resembling that of the aspartyl and seryl enzymes, a C-terminal anticodon recognition domain of 100 residues and a third domain unusually inserted between motifs 1 and 2 almost certainly interacting with the acceptor arm of tRNA(Gly). The C-terminal domain has a novel five-stranded parallel-antiparallel beta-sheet structure with three surrounding helices. The active site residues most probably responsible for substrate recognition, in particular in the Gly binding pocket, can be identified by inference from aspartyl-tRNA synthetase due to the conserved nature of the class II active site , .; GO: 0000166 nucleotide binding, 0004820 glycine-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006426 glycyl-tRNA aminoacylation, 0005737 cytoplasm.

PheRS belongs to class II aminoacyl-tRNA synthetases (aaRS) based upon its structure. While class II aaRSs generally aminoacylate the 3'-OH ribose of the appropriate tRNA, PheRS is an exception in that it attaches the amino acid at the 2'-OH group, like class I aaRSs. PheRS is an alpha-2/ beta-2 tetramer. While the alpha chain contains a catalytic core domain, the beta chain has a non-catalytic core domain.

1.1. from EC) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology . The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric . Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices , and are mostly dimeric or multimeric, containing at least three conserved regions , , . However, tRNA binding involves an alpha-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases . Prolyl-tRNA synthetase is a class II tRNA synthetase and is recognized by IPR002314 from INTERPRO, which recognises tRNA synthetases for Gly, His, Ser, and Pro. The prolyl-tRNA synthetases are divided into two widely divergent families. This family includes the archaeal enzyme, the Pro-specific domain of a human multifunctional tRNA ligase, and the enzyme from the spirochete Borrelia burgdorferi (Lyme desease spirochete). The other family, IPR004500 from INTERPRO, includes enzymes from Escherichia coli, Bacillus subtilis, Synechocystis sp. (strain PCC6803), and one of the two prolyl-tRNA synthetases of Saccharomyces cerevisiae (Baker's yeast).; GO: 0000166 nucleotide binding, 0004827 proline-tRNA ligase activity, 0005524 ATP binding, 0006412 translation, 0006433 prolyl-tRNA aminoacylation, 0005737 cytoplasm.